Method and system for testing an overspeed protection system of a powerplant

ABSTRACT

Embodiments of the present invention have the technical effect of automatically testing an overspeed protection system associated with multiple powerplant machines of a powerplant. An embodiment of the present invention may automatically test the overspeed protection system while at least one of the powerplant machines is in the process of shutting down. Another embodiment of the present invention may automatically test the overspeed protection system by adjusting the speed of a shaft while at least one of the powerplant machines operates at full-speed-no-load.

This application is related to commonly-assigned U.S. patent applicationSer. No. 11/584,095 [GE Docket 213935], filed Oct. 20, 2006; and U.S.patent application Ser. No. 11/589,579 [GE Docket 219837], filed Oct.30, 2006.

BACKGROUND OF THE INVENTION

The present invention relates to a protection system of a powerplant;and more particularly to a method and system for automated overspeedprotection on a powerplant comprising multiple powerplant machinesintegrated by at least one shaft.

Some powerplants are configured with multiple powerplant machines, suchas, but not limiting of, turbomachines, and others with rotating shafts.The powerplant configurations may include, but are not limited to, asteam turbine and a gas turbine integrated by a single shaft (commonlycalled a single-shaft STAG); or a multiple turbines integrated viamultiple shafts.

An overspeed condition occurs after the speed of a shaft on a powerplantmachine exceeds a specified range. During the overspeed condition, apowerplant machine typically experiences severe mechanical and thermalstresses that can cause a catastrophic failure.

Generally, the powerplant machine is equipped with protection systems,which attempt to reduce the effects of an overspeed condition. Agovernor system generally serves as the primary line of protection. Upondetecting an overspeed condition, the governor attempts to decrease thespeed of the shaft. There may also be a secondary, or independent line,of protection—an overspeed protection system. Typically, the overspeedprotection system incorporates mechanical, electrical, and softwarecomponents to safeguard the powerplant machine. An overspeed protectionsystem protects the powerplant machine by initiating an emergencyshutdown (commonly called a trip) during an overspeed event.

Powerplant operators periodically test the overspeed protection systemto determine if the system is functioning properly. Prior to testing theoverspeed protection system, the powerplant machine is customarilyoperating in a full-speed-no-load (FSNL) condition. FSNL is a conditionwhen the powerplant machine is at a normal operating speed and is notexporting energy to a load. An overspeed test typically involvesmanually raising the speed of a shaft above the normal operating range.For example, but not limiting of, during an overspeed test operators mayraise the speed of the shaft to 110% of the normal operating speed;thereafter the overspeed protection system should trip the powerplantmachine.

There are a few problems with the current method of overspeed testing.Manually adjusting the shaft speed may introduce high thermaltransients. A trip at a speed near or above the normal operating speedcan introduce large mechanical, electrical, and thermal stresses on thecomponents of the powerplant machine. These stresses decrease themaintenance interval. Moreover, after a trip, a re-start of thepowerplant machine is required, which delays the exporting of energy. Inaddition, the current overspeed testing methods typically require thatthe powerplant machine operate at FSNL. This does not generate revenuebut consumes fuel and electricity. These problems drive powerplantmachine operators to avoid manual speed adjustments, trips, FSNLoperation, and overspeed testing.

For the foregoing reasons, there is a need for a method of testing anoverspeed protection system that reduces the chance of a trip. Themethod should be adaptable to a wide variety powerplants, such as, butnot limiting of, a single shaft STAG.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with an embodiment of the present invention, a method oftesting an overspeed protection system of a powerplant, the methodcomprising: providing a powerplant comprising multiple powerplantmachines operationally integrated by a shaft that rotates duringoperation of the multiple powerplant machines; providing an overspeedprotection system configured for detecting an overspeed event associatedwith the shaft; selecting a methodology for testing the overspeedprotection system; wherein the methodology determines whether themultiple powerplant machines are operating in a shutdown mode or anoperating mode; determining whether the speed of the shaft exceeds ashutdown value representative of the overspeed event, if the multiplepowerplant machines are in the shutdown mode; determining whether thespeed of the shaft exceeds an overspeed trip value representative of theoverspeed event, if the multiple powerplant machines are in theoperating mode; changing the overspeed trip value; and determiningwhether the overspeed protection system would operate to trip themultiple powerplant machines; wherein the method reduces the possibilityof a trip occurring during testing of the overspeed protection system.

In accordance with an alternate embodiment of the present invention, amethod of testing an overspeed protection system of a powerplant, themethod comprising: providing a powerplant comprising a gas turbine and asteam turbine, and wherein a shaft integrates the gas turbine and thesteam turbine forming a steam and gas powertrain (STAG); providing anoverspeed protection system configured for detecting an overspeed eventassociated with the shaft; selecting a methodology for testing theoverspeed protection system; wherein the methodology determines whetherthe STAG is operating in a shutdown mode or an operating mode;determining whether the speed of the shaft exceeds a shutdown valuerepresentative of the overspeed event, if the STAG is in the shutdownmode; determining whether the speed of the shaft exceeds an overspeedtrip value representative of the overspeed event, if the STAG is in theoperating mode; changing the overspeed trip value; and determiningwhether the overspeed protection system would operate to trip the STAG;wherein the method reduces the possibility of a STAG trip during testingof the overspeed protection system.

In accordance with another alternate embodiment of the presentinvention, a system configured for testing an overspeed protectionsystem of a powerplant, the method comprising: a powerplant comprising agas turbine, a steam turbine, and a shaft; wherein the shaft comprisesmultiple components and integrates the gas turbine and the steam turbineforming a steam and gas powertrain (STAG); a control system comprisingan overspeed protection system, wherein the control system is configuredfor detecting an overspeed event associated with the shaft; and performsthe steps of: a) selecting a methodology for testing the overspeedprotection system; wherein the methodology determines whether the STAGis operating in a shutdown mode or an operating mode; and wherein themethodology comprises a shutdown mode procedure configured for theshutdown mode, and an operating mode procedure configured for theoperating mode; b) determining whether the speed of the shaft exceeds ashutdown value representative of the overspeed event, if the STAG is inthe shutdown mode; c) determining whether the speed of the shaft exceedsa overspeed trip value representative of the overspeed event, if theSTAG is in the operating mode; d) changing the overspeed trip value; ande) determining whether the overspeed protection system would operate totrip the STAG; wherein the method reduces the possibility of a STAG tripduring testing of the overspeed protection system.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic illustrating the environment in which anembodiment of the present invention operates.

FIG. 2 is a schematic illustrating a method of testing an overspeedprotection system in accordance with an embodiment of the presentinvention.

FIGS. 3A-3B (collectively FIG. 3) are flowcharts illustrating an exampleof a method of testing an overspeed protection system during a shutdownsequence, of FIG. 2, in accordance with an embodiment of the presentinvention.

FIGS. 4A-4C (collectively FIG. 4) are schematics illustrating themethods of FIGS. 2 and 3, in use, in accordance with an embodiment ofthe present invention.

FIGS. 5A and 5B (collectively FIG. 5) are flowcharts illustrating anexample of a second method of testing an overspeed protection system, ofFIG. 2, in accordance with an embodiment of the present invention.

FIGS. 6A-6E (collectively FIG. 6) are schematics illustrating themethods of FIGS. 2 and 5, in use, in accordance with an embodiment ofthe present invention.

FIG. 7 is a block diagram of an exemplary system for testing anoverspeed protection system in accordance with embodiments of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention has the technical effect of automatically testingan overspeed protection system associated with multiple powerplantmachines of a powerplant. An embodiment of the present invention mayautomatically test the overspeed protection system while at least one ofthe powerplant machines is shutting down. Another embodiment of thepresent invention may automatically test the overspeed protection systemby adjusting the speed of a shaft while at least one of the powerplantmachines operates at FSNL.

Detailed example embodiments are disclosed herein. However, specificstructural and functional details disclosed herein are merelyrepresentative for purposes of describing example embodiments. Exampleembodiments may, however, be embodied in many alternate forms, andshould not be construed as limited to only the embodiments set forthherein.

Accordingly, while example embodiments are capable of variousmodifications and alternative forms, embodiments thereof are illustratedby way of example in the drawings and will herein be described indetail. It should be understood, however, that there is no intent tolimit example embodiments to the particular forms disclosed, but to thecontrary, example embodiments are to cover all modifications,equivalents, and alternatives falling within the scope of exampleembodiments.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of example embodiments. Asused herein, the term “and/or” includes any, and all, combinations ofone or more of the associated listed items.

The terminology used herein is for describing particular embodimentsonly and is not intended to be limiting of example embodiments. As usedherein, the singular forms “a”, “an” and “the” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”,“comprising”, “includes” and/or “including”, when used herein, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

It should also be noted that in some alternative implementations, thefunctions/acts noted might occur out of the order noted in the FIGS. Twosuccessive FIGS., for example, may be executed substantiallyconcurrently or may sometimes be executed in the reverse order,depending upon the functionality/operations involved.

The present invention may be applied to many forms of powerplantmachines, which may be considered a machine that transfers energy, inpart by rotating a shaft. The shaft integrates multiple powerplantmachines, allowing each powerplant machine to contribute to the torquethat rotates the shaft.

Embodiments of the present invention may apply to a wide variety ofpowerplant machines having the form of a rotating machine such as, butnot limiting of, radial, axial, centrifugal machines in open and/orclosed systems. This may include, but are not limited to, the following:axial turbines, axial compressors, centrifugal compressors, helicalscrew compressors, radial-inflow turbines, torque converters, pumps,fans, blowers, hydraulic turbines, marine propellers, wind turbines, orany combination thereof.

The powerplant machine may also have the form of a turbomachineconfigured for producing power and/or consuming power. Theseturbomachines may include, but are not limited to, combustion turbinesand steam turbines. These turbomachines may primarily function toincrease pressure of a working fluid. Non-limiting examples of theworking fluid including: air, water, gas, physical matter, or anycombination, thereof. These turbomachines may consume a wide variety ofenergy sources, such as, but not limiting of, gas, liquid fuel, air,water, vapor, wind, electricity, thermal, steam, or any combinationthereof.

Embodiments of the present invention may be applied to powerplantmachines operating in a wide variety of applications including, but notlimited of, the following: aerospace, automotive, refrigeration,heating, industrial, power generation, marine, chemical, agricultural,petrochemical, mechanical drives, pumps, fans blowers, compressors, andthe like.

Referring now to the FIGS., where the various numbers represent likeelements throughout the several views, FIG. 1 is a schematicillustrating an environment in which an embodiment of the presentinvention may operate. FIG. 1 illustrates a powerplant 100, in acombined cycle configuration, having a gas turbine 105 and a steamturbine 160. A shaft 137 integrates the gas and steam turbines, 105,160.This configuration is considered a single-shaft STAG powertrain.Although, the embodiments of the present invention are described hereinwith reference to a single-shaft STAG application, the present inventionmay be applied to other powerplant configurations having multiplepowerplant machines that may, or may not be, integrated by a singleshaft 137.

As discussed, the overspeed protection system serves as a second line ofdefense during an overspeed event; and incorporates mechanical,electrical, and software components to safeguard the powerplant machine.The overspeed protection system may include the stop/speed ration valve152 and the steam valves 162, which serve as the second line of defense.

The gas turbine 105 generally comprises a compressor section 110, acombustion system 120, a turbine section 125, and an exhaust section130. Generally, the compressor 110 ingests and compresses an inlet air,represented by an arrow in FIG. 1. The compressed air may flowdownstream to the combustion system 120, where the compressed air ismixed with a fuel, such as, but not limiting of, a natural gas, receivedfrom the gas fuel system 150, and then combusted. The energy releasedduring the combustion process flows downstream and drives the turbinesection 125. A load, such as, but not limiting of, a generator 167 maybe coupled to the gas turbine 105 via the shaft 137. Here, themechanical torque generated in the turbine section 125 drives thegenerator 167.

The exhaust 135 generated during the operation of the gas turbine 105may flow downstream through an exhaust section 130 and may be receivedby a heat recovery steam generator (HRSG) 140. The HRSG 140 utilizes aheat exchanging process to transfer some of the heat in the exhaust 135to condensate or feedwater 147, creating steam 145. The steam 145 mayflow downstream through the steam valves 162 to a steam turbine 160,coupled to gas turbine 105, via the shaft 137. After flowing through thesteam valves 162 and the steam turbine 160, the steam 145 may condensein a condensor 165, forming the condensate 147. A condensate orfeedwater pump (not illustrated) may then drive the condensate orfeedwater 147 into the HRSG 140, where the aforementioned process may berepeated. After flowing through the HRSG 140, the exhaust 135 may flowto the stack (not illustrated). As the steam 145 flows through the steamturbine 160, the energy of the steam 145 is transferred into mechanicaltorque that drives the shaft 137.

A control system 170 may monitor and control the operation of thepowerplant 100. In accordance with embodiments of the present invention,the control system 170 may implement the overspeed testing system asdescribed below.

As will be appreciated, the present invention may be embodied as amethod, system, or computer program product. Accordingly, the presentinvention may take the form of an entirely hardware embodiment, anentirely software embodiment (including firmware, resident software,micro-code, etc.) or an embodiment combining software and hardwareaspects all generally referred to herein as a “circuit”, “module,” or“system”. Furthermore, the present invention may take the form of acomputer program product on a computer-usable storage medium havingcomputer-usable program code embodied in the medium. As used herein, theterms “software” and “firmware” are interchangeable, and include anycomputer program stored in memory for execution by a processor,including RAM memory, ROM memory, EPROM memory, EEPROM memory, andnon-volatile RAM (NVRAM) memory. The above memory types are exemplaryonly, and are thus not limiting as to the types of memory usable forstorage of a computer program. Any suitable computer readable medium maybe utilized.

The computer-usable or computer-readable medium may be, for example butnot limited to, an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system, apparatus, device, or propagationmedium. More specific examples (a non exhaustive list) of thecomputer-readable medium would include the following: an electricalconnection having one or more wires, a portable computer diskette, ahard disk, a random access memory (RAM), a read-only memory (ROM), anerasable programmable read-only memory (EPROM or Flash memory), anoptical fiber, a portable compact disc read-only memory (CD-ROM), anoptical storage device, a transmission media such as those supportingthe Internet or an intranet, or a magnetic storage device. Note that thecomputer-usable or computer-readable medium could even be paper oranother suitable medium upon which the program is printed, as theprogram can be electronically captured, via, for instance, opticalscanning of the paper or other medium, then compiled, interpreted, orotherwise processed in a suitable manner, if necessary, and then storedin a computer memory. In the context of this document, a computer-usableor computer-readable medium may be any medium that can contain, store,communicate, propagate, or transport the program for use by or inconnection with the instruction execution system, apparatus, or device.

The term processor, as used herein, refers to central processing units,microprocessors, microcontrollers, reduced instruction set circuits(RISC), application specific integrated circuits (ASIC), logic circuits,and any other circuit or processor capable of executing the functionsdescribed herein.

Computer program code for carrying out operations of the presentinvention may be written in an object oriented programming language suchas Java7, Smalltalk or C++, or the like. However, the computer programcode for carrying out operations of the present invention may also bewritten in conventional procedural programming languages, such as the“C” programming language, or a similar language. The program code mayexecute entirely on the user's computer, partly on the user's computer,as a stand-alone software package, partly on the user's computer andpartly on a remote computer or entirely on the remote computer. In thelatter scenario, the remote computer may be connected to the user'scomputer through a local area network (LAN) or a wide area network(WAN), or the connection may be made to an external computer (forexample, through the Internet using an Internet Service Provider).

The present invention is described below with reference to flowchartillustrations and/or block diagrams of methods, apparatuses (systems)and computer program products according to embodiments of the invention.It will be understood that each block of the flowchart illustrationsand/or block diagrams, and combinations of blocks in the flowchartillustrations and/or block diagrams, can be implemented by computerprogram instructions. These computer program instructions may beprovided to a processor of a public purpose computer, special purposecomputer, or other programmable data processing apparatus to produce amachine, such that the instructions, which execute via the processor ofthe computer or other programmable data processing apparatus, createmeans for implementing the functions/acts specified in the flowchartand/or block diagram block or blocks.

These computer program instructions may also be stored in acomputer-readable memory. These instructions can direct a computer orother programmable data processing apparatus to function in a particularmanner. This is such that the instructions stored in thecomputer-readable memory produce an article of manufacture includinginstruction means which implement the function/act specified in theflowchart and/or block diagram block or blocks. The computer programinstructions may also be loaded onto a computer or other programmabledata processing apparatus. These instructions may cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer implemented process. Here, theinstructions, which execute on the computer or other programmableapparatus, provide steps for implementing the functions/acts specifiedin the flowchart and/or block diagram blocks.

Referring again to the FIGS., FIG. 2 is a schematic illustrating amethod 200 of testing an overspeed protection system in accordance withan embodiment of the present invention. In an embodiment of the presentinvention, an operator may use the control system 170 to monitor and/orcontrol the operation of the method 200, via a graphical user interface(GUI) or the like.

In step 205, the powerplant 100 is in an operational mode. Here, thepowerplant 100 may be at FSNL, exporting power, or in a similaroperational mode.

In step 210, the method 200 may determine whether a test of theoverspeed protection system is desired. Here, an operator may use theGUI to indicate that a test of the overspeed protection system isdesired. If a test of the overspeed protection system is desired thenthe method 200 may proceed to step 215; otherwise the method 200 mayrevert to step 205.

In step 215, the method 200 may select a powerplant overspeed testingmethodology. A significant benefit of the present invention is theability to test the overspeed protection system via two methodologies.The shutdown methodology allows a user to test the overspeed protectionsystem while the powerplant machines are in the process of shuttingdown. The operating methodology allows a user to test the overspeedprotection system while the powerplant is operating at FSNL. Thefeatures and advantages of each methodology are discussed below. If thepowerplant is shutting down, then the method 200 may proceed to step220. If the speed of the shaft of the powerplant is around a normaloperating speed, then the method 200 may proceed to step 230.

In step 220, the method 200 may determine that the powerplant may beabout to commence and initiate a shutdown process.

In step 225, the method 200 may initiate a test of the overspeedprotection system while the powerplant is shutting down. FIGS. 3 and 4describe and illustrate the steps associated with testing the overspeedprotection system while the powerplant is shutting down.

In step 230, the method 200 may determine that the shaft speed of thepowerplant may be operating within a normal speed range.

In step 235, the method 200 may initiate a test of the overspeedprotection system while the powerplant may be at FSNL. FIGS. 5 and 6describe and illustrate the steps associated with testing the overspeedprotection system while the powerplant may be operating at FSNL.

Referring now to FIGS. 3A and 3B (collectively FIG. 3), which are aflowchart illustrating a method 300 of testing an overspeed protectionsystem during a shutdown sequence, in accordance with an embodiment ofthe present invention. In step 305, a fired shutdown of the gas turbine105 is initiated. The fired shutdown may be initiated manually by anoperator or automatically by a control system with requisite privileges.

In step 310, the method 300 determines whether at least one firedshutdown overspeed test permissive is satisfied. A user may configure aplurality of permissives that are prerequisites to testing. Thesepermissives may be used to ensure a specific operating state prior totesting. For example, but not limiting of, a user may prefer that thegas turbine 105 is operating at or near a FSNL state prior to commencingthe testing. If a required testing permissive is not satisfied, then themethod 300 may proceed to step 335; otherwise the method 300 may proceedto step 315.

In step 315, the fired shutdown overspeed test is selected. A user mayconfigure the method 300 to automatically select the test after step 310is satisfied. A user may desire this option if the operation of the gasturbine 105 is conducted remotely. In the alternative, a user may preferto manually select the test, which may be desirable if the operation ofthe turbine is conducted locally.

The method 300 may then proceed to step 320, which may determine if theactual speed of the shaft 137 exceeds the combustor flameout speed. Ifthe actual speed exceeds the flameout speed, then the method 300 mayproceed to step 325; otherwise the method 300 may proceed to step 335.The present invention allows the user to configure a parameter fordetermining the combustor flameout speed. For example, a user may setthe combustor flameout speed as a control constant. Alternatively, thepresent invention allows the combustor flameout speed to be a variableautomatically determined during testing.

The method 300, in step 325, determines whether the test permissive ofstep 310 is maintained. Operational events may cause the test permissiveto change state. For example, a fuel system issue may lead to apremature flameout and loss of the test permissive. If the testpermissive is not maintained, then the method 300 may proceed to step335; otherwise the method 300 may proceed to step 330.

In step 330 the user may manually abort the test. A user may discover areason, operationally or otherwise, for aborting the test. For example,a user may discover that a flame detector is not providing a reliableindication of flame status; and flame status may be an important testingrequirement. If the user aborts the test, then the method 300 mayproceed to step 335; otherwise the method 300 may proceed to step 340.

In step 335, the method 300 aborts the test. After the test is aborted,the gas turbine 105 operation reverts to the previous fired shutdownsequence. A user may configure the method 300 to provide a notificationthat the testing was aborted. The notification may be an alarm ofvarying forms such as, but not limited to, an audio signal, a graphic,or a text message.

In step 340, illustrated in FIG. 3B, the overspeed trip set point ischanged to a fired shutdown trip set point. The value of the firedshutdown trip set point may be influenced by a variety of mechanical,operational, and reliability factors. These factors may vary amongpowerplant machine types, combustion systems, operational conditions,fuel types, etc. The value is typically set to near the natural flameout speed of the particular combustion system, thereby minimizing thethermal transients associated with a trip. An embodiment of the presentinvention allows the user to input the fired shutdown trip set pointvalue, thereby providing an adjustment means for specific conditions.Alternatively, the present invention may be configured to automaticallygenerate, and input a value for the fired shutdown trip set point.

After the overspeed trip set point is changed, the method 300 mayproceed to step 345. Here, the gas turbine 105 may experience a firedshutdown overspeed trip. The trip may occur after the actual speed ofthe gas turbine 105 is near the fired shutdown overspeed set point.

The method 300, in step 350, may then determine whether the emergencyprotection system functioned correctly. In a gas turbine 105, theemergency protection system generally operates to rapidly stop the fuelflow to the combustion system, thereby extinguishing combustion. In thesteam turbine 160, the emergency protection system generally operates torapidly stop steam flow by closing the steam valves 162. This minimizesthe amount of torque produced by the steam turbine 160 for the shaft137. Data recording means are typically used to verify that thecomponents of the emergency protection system operated correctly. If theemergency protection system functioned correctly, then the method 300may proceed to step 355, where the fired shutdown test is successful;otherwise the method 300 may proceed to step 360, where the firedshutdown test is unsuccessful. The present invention may be integratedwith an alarm system that notifies the user whether or not the emergencyprotection system functioned correctly.

FIGS. 4A-4C (collectively FIG. 4) are schematics illustrating themethods of FIGS. 2 and 3, in use, in accordance with an embodiment ofthe present invention. FIG. 4 illustrates the gas turbine 105 and thesteam turbine 160 of the powerplant 100 illustrated in FIG. 1. FIG. 4also illustrates pertinent operational parameters of the gas turbine 105and the steam turbine 160. These parameters include actual turbine speed410 (as a percentage of normal operating speed); overspeed trip setpoint (as a percentage of normal operating speed) 420; and flamedetectors of the combustion system 120. FIG. 4 also illustrates the gasfuel system 150 with a stop/speed ratio valve 152, a plurality of gascontrol valves 154, and the steam valves 162.

Referring specifically to FIG. 4A, which illustrates that the actualturbine speed 410 is 100%, the overspeed trip set point 420 is 110%, andthe flame detector indicating flame. These parameters suggest that theturbine 100 is operating in a FSNL condition.

After a fired shutdown is initiated and the test permissive(s) issatisfied, the user may commence the fired shutdown overspeed testing.FIG. 4B illustrates the gas turbine 105 experiencing a fired shutdownwith the actual turbine speed 410 at 50% and flame detector indicatingflame. The present invention allows the user to manually abort the test,thereby resuming the fired shutdown on the gas turbine 105.

The fired shutdown overspeed test automatically adjusts the overspeedtrip set point 420 to a value near the flameout speed of the turbine100. Here, the set point 420 is lowered to 48%.

Soon after the set point 420 is changed, the overspeed protection systemshould trip the gas turbine 105 and steam turbine 160, as illustrated inFIG. 4C. The trip of the gas turbine 105 and steam turbine 160 rapidlyminimize torque transfer to the shaft 137. Here the combustion flame isextinguished and the steam valves 162 are closed. FIG. 4C illustratesthat the flame detector, of the combustion system 120, does not indicatea flame presence. After the gas turbine 105 and the steam turbine 160trip, the overspeed trip set point 420 may automatically reset to adefault value.

Referring now to FIGS. 5A and 5B (collectively FIG. 5), which are aflowchart illustrating the steps for a method 500 of testing anoverspeed protection system of a turbine while the gas turbine 105initially operates at FSNL. In an embodiment of the present invention,an operator may use the control system 170 to monitor and/or control theoperation of the method 500, via a graphical user interface (GUI) or thelike.

The method 500 may include a biasing system or the like which adjuststhe default set points of the overspeed protection system trip and anemergency protection system trip. The biasing system may allow the speedof the shaft 137 to increase to the default setting of the overspeedtrip set point, without tripping the STAG. This may ensure that theoverspeed protection system is tested at the default setting of theoverspeed trip set point. Furthermore, an embodiment of the method 500may not disable the overspeed protection system or the emergencyprotection system. For example, but not limiting of, during testing, thebiasing system may increase the emergency trip set point from 110% to111% and the protection trip set point from 113% to 114%. Therefore, ifthe present invention were to malfunction, independent lines ofprotection may protect the STAG.

The present invention may require that at least one test permissive issatisfied and maintained by both the gas turbine 105 and the steamturbine 160 prior to the start of the overspeed test. These permissivesmay include a master protective trip state; a generator/driven loadstatus; an operating permissive; an inlet guide vane position; and astabilization permissive. Furthermore, each permissive may be requiredat a different period of the overspeed test. For example, an operatingpermissive may be required before the testing starts, whereas thestabilization permissive may be required during the testing.

In step 505, a gas turbine 105 and a steam turbine 160 may be operatingat FSNL, which may be a preferable starting condition for an overspeedtest. Typically, a gas turbine 105 and a steam turbine 160 operate atFSNL when not exporting energy to an external load. For example, beforesynchronizing the generator 167 to a utility grid, a gas turbine 105 anda steam turbine 160 operate at FSNL.

In step 510, the method 500 determines if an operating permissive issatisfied. An embodiment of the present invention may allow the user toconfigure at least one operating permissive. The operating permissivemay include continuous operation at FSNL, a soak time, or the likerequirement. For example, the permissive may require a longer operationperiod for a new shaft. If the operating permissive is satisfied, thenthe method 500 may proceed to step 515; otherwise the method 500 mayrevert to step 505.

In step 515, the method 500 determines whether at least one overspeedtest permissive is satisfied. Similar to step 510, an embodiment of thepresent invention may allow the user to define the overspeed testpermissive or define a plurality of overspeed test permissives. Forexample, but not limiting of, the overspeed test permissive may include:an inlet guide vane position; a compressor protection system status; andan inlet air system status, inlet bleed heat, or the like. If theoverspeed test permissive is not satisfied, then the method 500 mayproceed to step 530; otherwise the method 500 may proceed to step 520.

In step 530, the method 500 may automatically abort the overspeed test.After the test is aborted, operation of the gas turbine 105 and thesteam turbine 160 automatically revert to FSNL. A user may configure themethod 500 to provide a notification that the test was aborted. Thenotification may be an alarm of varying forms such as, but not limitedto, an audio signal, a graphic, or a text message.

The method 500 may proceed to step 520, where the overspeed test isinitiated. A user may pre-configure the method 500 to automaticallyinitiate the overspeed test after step 515 is satisfied. A user maydesire this option if, for example, the operation of the gas turbine 105and the steam turbine 160 are conducted remotely. Alternatively, themethod 500 may be pre-configured to require a user action to initiatethe overspeed test. The user action may be, but is not limited to,selecting an “overspeed test initiate” button, or the like, on a displaywhere the turbines 105,160 are locally controlled.

In step 525, the method 500 may determine whether a stabilizationpermissive is satisfied. The stabilization permissive may ensure thatthe gas turbine 105 is operating near a thermal steady state withminimal heat transients. The stabilization permissive may be in the formof a timer, or the like, which counts the gas turbine 105 operatingtime. Similar to steps 510 and 515, an embodiment of the presentinvention may allow the user to define a stabilization permissive or aplurality of stabilization permissives. Furthermore, the stabilizationpermissive may vary among types and/or classes of gas turbine 105. Ifthe stabilization test permissive is not satisfied, then the method 500may proceed to step 530; otherwise the method 500 may proceed to step535.

In step 535, the method 500 may select an automatic speed increase. Anembodiment of the present invention may notify the user that the method500 is ready for the automatic increase. This notification may be, butis not limited to, an alarm and/or a prompt requiring a user action toproceed with the automatic speed increase. Alternatively, an embodimentof the present invention may be pre-configured to automatically selectthe automatic speed increase.

In step 540, the method 500 may automatically increase the speed of theshaft 137, which integrates the gas turbine 105 and the steam turbine160. An embodiment of the present invention may vary the rate at whichthe speed increases, thereby allowing a user to minimize the thermaltransients commonly associated with speed increases. The rate may varydepending on turbine class and operational environment. For example, anembodiment of the present invention may also allow the user to vary therate during the overspeed testing to account for the momentum associatedwith the shaft and other mechanical components. Furthermore, arelatively faster rate may be used during lower speeds and a slower rateused as the turbine nears the overspeed trip set point.

After the automatic speed increases commence, the method 500, in step545, may determine whether the user decides to manually abort theoverspeed test. A reason for aborting the overspeed test may include,but is not limited to, operational issues. For example, the higher shaftspeeds may cause a vibration concern, requiring the user to abort thetest. If the user aborts the overspeed test, then the method 500 mayproceed to step 550; otherwise the method 500 may proceed to step 555.

In step 550, the method 500 aborts the test. Similar to step 530, afterthe overspeed test is aborted, operation of the gas turbine 105 and thesteam turbine 160 may revert to FSNL. A user may configure the method500 to provide a notification that the overspeed test was aborted duringstep 545. The notification may be an alarm of varying forms such as, butis not limited to, an audio signal, a graphic, or a text message.

The present invention may incorporate a control system, turbinecontroller, or the like; that operates turbines 105,160. The turbinecontroller(s) may include at least one processing system, commonlycalled a core, which registers the speed of the turbines 105,160. Anembodiment of the present invention may include a turbine controllerhaving at least two cores, an operation core, and a protection core, orthe like. The method 500, in step 555, allows the user to pre-configureeach core to register the speeds of the gas turbine 105 and the steamturbine 160. This serves to verify that the gas turbine 105 and thesteam turbine are each experiencing an overspeed condition.

The gas turbine 105 may include a protection system that generallyoperates to rapidly stop the fuel flow to the combustion system, therebyextinguishing combustion. In the steam turbine 160, the emergencyprotection system generally operates to rapidly stop steam flow byclosing the steam valves 162. This minimizes the amount of torqueproduced by the steam turbine 160 for the shaft 137. Data recordingmeans are typically used to verify that the protection system componentsoperated correctly during the overspeed test. The present invention maybe integrated with an alarm system that notifies the user whether or notthe protection system would have operated correctly in the event of areal overspeed condition.

In step 555, the method 500 may determine whether the shaft speedexceeds the overspeed trip set point. In an embodiment of the presentinvention, if the operation core and protection core do not registerthat the shaft speed exceeds the overspeed trip set point, then themethod 500 may proceed to step 560; otherwise the method 500 may proceedto step 570.

An embodiment of the present invention may increase the speed of theshaft by first increasing a speed reference. The speed reference isconverted to a fuel stroke reference, or the like, which eventuallyincreases the speed of the shaft. In step 560, the method 500 determinesif the turbine controller is initiating a speed reference greater thanthe overspeed trip set point. If the speed reference is not greater thanthe overspeed trip set point, then the method 500 may revert to step540. Alternatively, if the speed reference is greater than the overspeedtrip set point, then the method 500 may proceed to step 565.

In step 565, the overspeed test is aborted to avoid a trip or acatastrophic failure that may be caused by a variety of reasons. Onereason for a catastrophic failure involves the thermal growth rates,which vary between the rotating and stationary turbine components.Generally, as the shaft speed increases, there is an increase in thethermal expansion of the components. Moreover, relatively tightclearances exist between the rotating and stationary turbine components,which are often made of different materials. These clearances maydecrease further as the rotating and stationary components grow duringthe overspeed testing. Hence, to avoid a catastrophic failure resultingfrom contact among rotating and stationary turbine components, themethod 500, in step 565 may abort the overspeed speed testing if thespeed reference exceeds the overspeed trip set point, even though theturbine speed is registering below the overspeed trip set point.

In step 570, the method 500 automatically decreases the shaft speed.Similar to step 540, an embodiment of the present invention may vary therate at which the speed decreases, thereby allowing a user to minimizethe thermal transients commonly associated with speed decreases. Forexample, but not limiting, of the rate may vary depending on turbineclass and operational environment. An embodiment of the presentinvention may also allow the user to vary the rate of speed decrease.For example, a relatively faster rate may be used during higher shaftspeeds and a slower rate used as the shaft speed nears the normaloperating speed.

The overspeed test of the present invention may be considered completewhen the shaft speed returns to around the normal operating speed. Instep 575, the method 500 may disable the automatic speed changes afterthe shaft speed returns to around FSNL.

Referring now to FIGS. 6A-6E (collectively FIG. 6), which are schematicsillustrating the environment in which an embodiment of the method 500may operate. FIG. 6 illustrates the gas turbine 105 and the steamturbine 160 experiencing a test of the overspeed protection system, inaccordance with an embodiment of the present invention. FIG. 6 alsoillustrates operational parameters of the gas turbine 105 and the steamturbine 160. These parameters include actual turbine speed 610 (as apercentage of normal operating speed); overspeed trip set point (as apercentage of normal operating speed) 620; and flame detector of thecombustion system 120. FIG. 6 also illustrates a gas fuel system 150having a stop/speed ratio valve 152, a plurality of gas control valves154, and the steam valves 162.

Referring specifically to FIG. 6A, which illustrates that the actualturbine speed 610 is 100%, the overspeed trip set point 620 is 110%,flame detector indicating flame. These parameters suggest that the gasturbine 105 and the steam turbine 160 may be operating in a FSNLcondition. After the testing permissive(s) is satisfied, the user maycommence the overspeed test.

FIG. 6B illustrates that after the overspeed test has commenced theactual turbine speed 610 increased to 103% and the overspeed trip setpoint 620 is biased to 111%. The present invention automatically adjuststhe speed of the shaft 137 during the overspeed test.

FIG. 6C illustrates the actual speed of the shaft 137 to be 110%, equalto that of the default value of the overspeed trip setting. Asdiscussed, the overspeed trip set point 620 is biased to 111%. Thepresent invention does not trip the gas turbine 105 or the steam turbine160 during the overspeed test when an overspeed condition is reached. Anembodiment of the present invention may notify the user of the overspeedcondition. As illustrated in FIG. 6D, the present inventionautomatically decreases the speed of the shaft 137 after the overspeedcondition is reached. Here, the actual speed 610 has been automaticallylowered to 108%. Furthermore, the present invention may remove thebiasing of the overspeed trip after actual speed reaches the defaultvalue of the overspeed trip setting. Here, the overspeed trip set point620 is returned to the default value of 110%. As illustrated in FIG. 6E,an embodiment of the present invention may continue to automaticallyadjust the speed of the shaft 137 until FSNL is reached, therebycompleting the test. Thereafter, a user may resume normal operation ofthe powerplant 100.

FIG. 7 is a step diagram of an exemplary system 700 to automaticallytest the overspeed protection system, in accordance with embodiments ofthe present invention. The elements of the methods 300,500 may beembodied in and performed by the system 700. The system 700 may includeone or more user or client communication devices 702 or similar systemsor devices (two are illustrated in FIG. 7). Each communication device702 may be a computer system, a personal digital assistant, a cellularphone, or similar device capable of sending and receiving an electronicmessage.

The communication device 702 may include a system memory 704 or localfile system. The system memory 704 may include a read only memory (ROM)and a random access memory (RAM). The ROM may include a basicinput/output system (BIOS). The BIOS may contain basic routines thathelp to transfer information between elements or components of thecommunication device 702. The system memory 704 may contain an operatingsystem 706 to control overall operation of the communication device 702.The system memory 704 may also include a browser 708 or web browser. Thesystem memory 704 may also include data structures 710 orcomputer-executable code to automatically test the overspeed protectionsystem that may be similar or include elements of the methods 300, 500.The system memory 704 may further include a template cache memory 712,which may be used in conjunction with the methods 300,500 toautomatically store data from the most recent test.

The communication device 702 may also include a processor or processingunit 714 to control operations of the other components of thecommunication device 702. The operating system 706, browser 708, datastructures 710 may be operable on the processor 714. The processor 714may be coupled to the memory system 704 and other components of thecommunication device 702 by a system bus 716.

The communication device 702 may also include multiple input devices,output devices or combination input/output devices 718. Eachinput/output device 718 may be coupled to the system bus 716 by aninput/output interface (not shown in FIG. 7). The input and outputdevices or combination I/O devices 718 permit a user to operate andinterface with the communication device 702 and to control operation ofthe browser 708 and data structures 710 to access, operate and controlthe software to automatically test the overspeed protection system. TheI/O devices 718 may include a keyboard and computer pointing device orthe like to perform the operations discussed herein.

The I/O devices 718 may also include disk drives, optical, mechanical,magnetic, or infrared input/output devices, modems or the like. The I/Odevices 718 may be used to access a medium 720. The medium 720 maycontain, store, communicate or transport computer-readable orcomputer-executable instructions or other information for use by or inconnection with a system, such as the communication devices 702.

The communication device 702 may also include or be connected to otherdevices, such as a display or monitor 722. The monitor 722 may be usedto permit the user to interface with the communication device 702. Themonitor 722 present images, graphics, or the like, which may begenerated by the data structures 710 for automatically testing theoverspeed protection system.

The communication device 702 may also include a hard disk drive 724. Thehard drive 724 may be coupled to the system bus 716 by a hard driveinterface (not shown in FIG. 7). The hard drive 724 may also form partof the local file system or system memory 704. Programs, software anddata may be transferred and exchanged between the system memory 704 andthe hard drive 724 for operation of the communication device 702.

The communication devices 702 may communicate with a remote server 726and may access other servers or other communication devices similar tocommunication device 702 via a network 728. The system bus 716 may becoupled to the network 728 by a network interface 730. The networkinterface 730 may be a modem, Ethernet card, router, gateway or the likefor coupling to the network 728. The coupling may be a wired connectionor wireless. The network 728 may be the Internet, private network, anintranet or the like.

The server 726 may also include a system memory 732 that may include afile system, ROM, RAM and the like. The system memory 732 may include anoperating system 734 similar to operating system 706 in communicationdevices 702. The system memory 732 may also include data structures 736to automatically test the overspeed protection system. The datastructures 736 may include operations similar to those described withrespect to the methods 300,500 for automatically testing the overspeedprotection system. The server system memory 732 may also include otherfiles 738, applications, modules and the like.

The server 726 may also include a processor 742 or a processing unit tocontrol operation of other devices in the server 726. The server 726 mayalso include I/O device 744. The I/O devices 744 may be similar to I/Odevices 718 of communication devices 702. The server 726 may furtherinclude other devices 746, such as a monitor or the like to provide aninterface along with the I/O devices 744 to the server 726. The server726 may also include a hard disk drive 748. A system bus 750 may connectthe different components of the server 726. A network interface 752 maycouple the server 726 to the network 728 via the system bus 750.

The flowcharts and step diagrams in the FIGS. illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present invention. In this regard, each step in theflowchart or step diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in thestep may occur out of the order noted in the figures. For example, twosteps shown in succession may, in fact, be executed substantiallyconcurrently, or the steps may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each step of the block diagrams and/or flowchart illustration, andcombinations of steps in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems which perform the specified functions or acts, or combinationsof special purpose hardware and computer instructions.

As one of ordinary skill in the art will appreciate, the many varyingfeatures and configurations described above in relation to the severalexemplary embodiments may be further selectively applied to form theother possible embodiments of the present invention. Those in the artwill further understand that all possible iterations of the presentinvention are not provided or discussed in detail, even though allcombinations and possible embodiments embraced by the several claimsbelow or otherwise are intended to be part of the instant application.In addition, from the above description of several exemplary embodimentsof the invention, those skilled in the art will perceive improvements,changes, and modifications. Such improvements, changes, andmodifications within the skill of the art are also intended to becovered by the appended claims. Further, it should be apparent that theforegoing relates only to the described embodiments of the presentapplication and that numerous changes and modifications may be madeherein without departing from the spirit and scope of the application asdefined by the following claims and the equivalents thereof.

1. A method of testing an overspeed protection system of a powerplant,the method comprising: providing a powerplant comprising multiplepowerplant machines operationally integrated by a shaft that rotatesduring operation of the multiple powerplant machines; providing anoverspeed protection system configured for detecting an overspeed eventassociated with the shaft; selecting a methodology for testing theoverspeed protection system; wherein the methodology determines whetherthe multiple powerplant machines are operating in a shutdown mode or anoperating mode; determining whether the speed of the shaft exceeds ashutdown value representative of the overspeed event, if the multiplepowerplant machines are in the shutdown mode; determining whether thespeed of the shaft exceeds an overspeed trip value representative of theoverspeed event, if the multiple powerplant machines are in theoperating mode; changing the overspeed trip value; and determiningwhether the overspeed protection system would operate to trip themultiple powerplant machines; wherein the method reduces the possibilityof a trip occurring during testing of the overspeed protection system.2. The method of claim 1, wherein the multiple powerplant machinescomprise a gas turbine and a steam turbine, and wherein the shaftintegrates the gas turbine and the steam turbine forming a steam and gaspowertrain (STAG).
 3. The method of claim 2, wherein the methodologycomprises a shutdown mode procedure configured for the shutdown mode,and an operating mode procedure configured for the operating mode. 4.The method of claim 3, wherein the shutdown mode procedure performs thesteps of: a. determining whether a testing permissive is satisfied; b.initiating a fired shutdown overspeed test; c. aborting the firedshutdown overspeed test if the speed of the shaft does not exceed aflameout speed; and d. changing an overspeed trip set point to a firedshutdown trip set point.
 5. The method of claim 4, wherein an emergencyprotection system controls a governor system associated with the gasturbine and the steam turbine, wherein the governor system partiallycontrols a speed and an acceleration of the shaft.
 6. The method ofclaim 5, further comprising the step of aborting the fired shutdownoverspeed test if the testing permissive is not maintained.
 7. Themethod of claim 6 further comprising the step of determining whether theemergency protection system controls the operation of the gas turbineand the steam turbine.
 8. The method of claim 3, wherein the operatingmode procedure performs the steps of: a. automatically adjusting thespeed of the shaft to approximately the overspeed trip value; b.determining if the speed of the shaft is approximately the overspeedtrip value; and c. automatically adjusting the speed of the shaft toapproximately an operating speed after determining if the speed of theshaft is approximately the overspeed trip value.
 9. The method of claim8, further comprising the steps of: a. initiating an overspeed test; b.determining whether a stabilization permissive is satisfied, otherwiseaborting the overspeed test if the stabilization permissive is notsatisfied; c. automatically adjusting the speed of the shaft; d.determining whether the speed of the shaft exceeds an overspeed tripvalue; e. determining whether a shaft speed reference exceeds theoverspeed trip value; f. aborting the overspeed test if the shaft speedreference exceeds the overspeed trip value while the speed of the shaftis below the overspeed trip value; and g. automatically disabling theautomatic adjustment of the speed of the shaft.
 10. The method of claim9, wherein the step of aborting the overspeed test adjusts the speed ofthe shaft to approximately an operating speed.
 11. The method of claim10 further comprising determining whether an operating permissive issatisfied.
 12. The method of claim 11 further comprising determiningwhether an overspeed test permissive is satisfied.
 13. The method ofclaim 12 further comprising biasing an overspeed trip set point.
 14. Amethod of testing an overspeed protection system of a powerplant, themethod comprising: providing a powerplant comprising a gas turbine and asteam turbine, and wherein a shaft integrates the gas turbine and thesteam turbine forming a steam and gas powertrain (STAG); providing anoverspeed protection system configured for detecting an overspeed eventassociated with the shaft; selecting a methodology for testing theoverspeed protection system; wherein the methodology determines whetherthe STAG is operating in a shutdown mode or an operating mode;determining whether the speed of the shaft exceeds a shutdown valuerepresentative of the overspeed event, if the STAG is in the shutdownmode; determining whether the speed of the shaft exceeds an overspeedtrip value representative of the overspeed event, if the STAG is in theoperating mode; changing the overspeed trip value; and determiningwhether the overspeed protection system would operate to trip the STAG;wherein the method reduces the possibility of a STAG trip during testingof the overspeed protection system.
 15. The method of claim 14, whereinthe methodology comprises a shutdown mode procedure configured for theshutdown mode, and an operating mode procedure configured for theoperating mode.
 16. The method of claim 15, wherein the shutdown modeprocedure performs the steps of: a. determining whether a testingpermissive is satisfied; b. initiating a fired shutdown overspeed test;c. aborting the fired shutdown overspeed test if the speed of the shaftdoes not exceed a flameout speed; and d. changing an overspeed trip setpoint to a fired shutdown trip set point.
 17. The method of claim 16,wherein the operating mode procedure performs the steps of: a.automatically adjusting the speed of the shaft to approximately theoverspeed trip value; b. determining if the speed of the shaft isapproximately the overspeed trip value; c. automatically adjusting thespeed of the shaft to approximately an operating speed after determiningif the speed of the shaft is approximately the overspeed trip value; d.initiating an overspeed test; e. determining whether a stabilizationpermissive is satisfied, otherwise aborting the overspeed test if thestabilization permissive is not satisfied; f. automatically adjustingthe speed of the shaft; g. determining whether the speed of the shaftexceeds an overspeed trip value; h. determining whether a shaft speedreference exceeds the overspeed trip value; i. aborting the overspeedtest if the shaft speed reference exceeds the overspeed trip value whilethe speed of the shaft is below the overspeed trip value; and j.automatically disabling the automatic adjustment of the speed of theshaft.
 18. A system configured for testing an overspeed protectionsystem of a powerplant, the method comprising: a powerplant comprising agas turbine, a steam turbine, and a shaft; wherein the shaft comprisesmultiple components and integrates the gas turbine and the steam turbineforming a steam and gas powertrain (STAG); a control system comprisingan overspeed protection system, wherein the control system is configuredfor detecting an overspeed event associated with the shaft; and performsthe steps of: a. selecting a methodology for testing the overspeedprotection system; wherein the methodology determines whether the STAGis operating in a shutdown mode or an operating mode; and wherein themethodology comprises a shutdown mode procedure configured for theshutdown mode, and an operating mode procedure configured for theoperating mode; b. determining whether the speed of the shaft exceeds ashutdown value representative of the overspeed event, if the STAG is inthe shutdown mode; c. determining whether the speed of the shaft exceedsa overspeed trip value representative of the overspeed event, if theSTAG is in the operating mode; d. changing the overspeed trip value; ande. determining whether the overspeed protection system would operate totrip the STAG; wherein the method reduces the possibility of a STAG tripduring testing of the overspeed protection system.
 19. The system ofclaim 18, wherein the control system executing the shutdown modeprocedure performs the steps of: a. determining whether a testingpermissive is satisfied; b. initiating a fired shutdown overspeed test;c. aborting the fired shutdown overspeed test if the speed of the shaftdoes not exceed a flameout speed; and d. changing an overspeed trip setpoint to a fired shutdown trip set point.
 20. The system of claim 18,wherein the control system executing the operating mode procedureperforms the steps of: a. automatically adjusting the speed of theshaft; b. determining whether the speed of the shaft is the overspeedtrip value; c. automatically adjusting the speed of the shaft to aboutan operating speed after automatically adjusting the speed of the shaftand determining whether the speed of the shaft is the overspeed tripvalue; d. initiating an overspeed test; e. determining whether astabilization permissive is satisfied, otherwise aborting the overspeedtest; f. automatically adjusting the speed of the shaft; g. determiningwhether the speed of the shaft exceeds an overspeed trip value, h.determining whether a shaft speed reference exceeds the overspeed tripvalue, otherwise aborting the overspeed test; and i. automaticallydisabling the automatic adjustment of the speed of the shaft.